Methods of refurbishing components of a fuel cell stack

ABSTRACT

Methods for refurbishing components, such as interconnects of a fuel cell stack, include singulating the stack and removing the electrolyte, seals and oxide layer using non-mechanical methods. The various methods of may be used either singly or in combination.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to U.S. ProvisionalApplication No. 61/478,697, filed Apr. 25, 2011, the entire contents ofwhich are incorporated herein by reference.

FIELD

The present invention is directed to fuel cell stacks, specifically tomethods of refurbishing stack components, such as interconnects.

BACKGROUND

A typical solid oxide fuel cell (SOFC) stack includes multiple fuelcells separated by interconnects (IC) which provide both electricalconnection between adjacent cells in the stack and channels for deliveryand removal of fuel and oxidant. When hydrocarbons are used for fuel,some of the hydrocarbons may catalytically decompose or crack on thesurface of the interconnect, leaving a deposit of coke. These cokedeposits can clog the channels adversely affecting the performance ofthe fuel cell stack.

The fuel cell stack may be reconditioned, however, by refurbishing theinterconnects. A typical IC refurbishment process may include thefollowing steps: (1) singulation (separating ICs/individual fuel cellsfrom one another), (2) removal of electrolyte debris from the IC, (3)removal of any other remaining internal stack components (if any) fromthe IC and (4) removal of high temperature adhesives, seals andprotective coatings.

Prior singulation method includes mechanically prying the stack apart.This process is time-consuming and prone to damaging the interconnects,by chipping, cracking, or inducing camber (curvature).

After singulation, most of the electrolyte can be scraped off, butmaterial left around the seal region is typically very well adhered tothe IC and hard to remove. The last step to achieving a clean part istypically removing the metal oxide (e.g., chromium oxide) that grows onthe fuel side of the chromium alloy IC and residual oxide seal material.A grit blasting process typically used in removing these oxides iscostly, time consuming, difficult to control, and can cause damage tothe part by inducing camber and excessive erosion of the part.

SUMMARY

Embodiments include methods for singulating a fuel cell stack thatcomprise connecting at least one conduit extending through multiplelayers of a fuel cell stack to a fluid source, applying fluid in theconduit through at least one first layer of the fuel cell stack,blocking the conduit in a second layer of the fuel cell stack, andremoving the second layer from the fuel cell stack.

Further embodiments include a method of singulating a fuel cell stack,comprising providing the fuel cell stack comprising a plurality oflayers, and singulating the fuel cell stack using a non-mechanicalmethod to remove at least one layer of the plurality of layers from thefuel cell stack.

Further embodiments include a method of removing fuel cell debris from asingulated fuel cell interconnect, comprising providing the interconnectsingulated from a fuel cell stack, and non-mechanically removing atleast part of the fuel cell debris from the interconnect.

Further embodiments include methods for singulating a fuel cell stackthat comprise providing an induction heating coil proximate to a layerof a fuel cell stack, inductively heating the layer, and removing thelayer from the fuel cell stack.

Further embodiments include methods for singulating a fuel cell stackthat comprise introducing the fuel cell stack to a reducing gascontaining environment at an elevated temperature, maintaining the fuelcell stack in the reducing gas containing environment at an elevatedtemperature for a period sufficient to weaken a bonding strength of aseal material, and removing at least one component from the fuel cellstack.

Further embodiments include methods for singulating a fuel cell stackthat comprise introducing the fuel cell stack to a chemical solutionconfigured to selectively remove a seal material from the stack,maintaining the fuel cell stack in the solution for a period sufficientto weaken a bonding strength of the seal material, removing at least onecomponent from the fuel cell stack.

Further embodiments include methods for singulating a fuel cell stackthat comprise directing radiation energy at a portion of the fuel cellstack to induce uneven heating in the stack, and removing at least onecomponent from the fuel cell stack.

Further embodiments include methods for singulating a fuel cell stackthat comprise directing acoustic energy at a portion of a stack, theacoustic energy having a frequency configured to damage a seal materialwithout damaging at least one other component of the stack, and removingthe at least one other component of the stack.

Further embodiments include methods of removing fuel cell debris from afuel cell interconnect that comprise annealing the interconnect in areducing-gas environment at a temperature from 850° C. to 1450° C., andremoving the debris from the interconnect.

Further embodiments include methods of removing fuel cell debris from afuel cell interconnect that comprise inductively heating theinterconnect, and removing the fuel cell debris.

Further embodiments include methods of removing fuel cell debris from afuel cell interconnect that comprise directing radiation energy at theinterconnect to induce non-uniform heating, and removing the fuel celldebris.

Further embodiments include methods of removing fuel cell debris from afuel cell interconnect that comprise heating the interconnect to atemperature from 850° C. to 1450° C., and removing the debris from theinterconnect.

Further embodiments include methods of removing oxide debris from a fuelcell interconnect that comprise treating the interconnect with achemical solution configured to selectively remove oxide materials.

Further embodiments include methods of removing oxide debris from a fuelcell interconnect that comprise electrochemically reducing an oxidematerial from a surface of the interconnect.

Further embodiments include methods of removing oxide debris from a fuelcell interconnect that comprise directing acoustic energy at theinterconnect, the acoustic energy having a frequency configured toshatter oxide debris material on the interconnect without damaging theinterconnect, and removing the oxide debris from the interconnect.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate example embodiments of theinvention, and together with the general description given above and thedetailed description given below, serve to explain the features of theinvention.

FIGS. 1A-1C schematically illustrate a method and apparatus forsingulating components of a fuel cell stack using compressed fluidaccording to one embodiment.

FIG. 2 is a process flow diagram illustrating a method for singulating acomponent of a fuel cell stack using compressed fluid.

FIG. 3 schematically illustrates a method for singulating a fuel cellstack using inductive heating.

FIG. 4 is a process flow diagram illustrating an embodiment method forsingulating a fuel cell stack by annealing the stack in a reducing gasenvironment.

FIG. 5 schematically illustrates a method for singulating a fuel cellstack using radiation energy.

FIG. 6 is a front view of an interconnect illustrating the effect of ahydrofluoric acid (HF) treatment on removal of a fuel cell electrolytefrom the interconnect.

DETAILED DESCRIPTION

The various embodiments will be described in detail with reference tothe accompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.References made to particular examples and implementations are forillustrative purposes, and are not intended to limit the scope of theinvention or the claims.

Various embodiments include methods for refurbishing components, such asinterconnects (ICs), of a fuel cell stack, such as a solid oxide fuelcell (SOFC) stack. Embodiments include methods of singulating,electrolyte removal, and seal, adhesive and coating removal. The variousmethods of singulating, electrolyte removal and seal, adhesive andcoating removal may be used either singly or in combination or incombination with conventional techniques.

An example of a fuel cell stack 100 is illustrated in FIGS. 1A-1C. Thefuel cell stack 100 comprises a plurality of layers 101A-101L, whereeach layer may comprise an interconnect. The layers 101A-101L may have aplanar configuration, such as shown in FIGS. 1A-1C, or other geometries,such as a tubular configuration. A plurality of fuel cells 102 (see FIG.1C) may be provided between each interconnect 101A-101L. In oneembodiment, each of the fuel cells 102 may comprise a solid oxide fuelcell (SOFC), which may include a solid oxide electrolyte material havinga cathode electrode on a first (e.g., air-side) surface and an anodeelectrode on a second (e.g., fuel-side) surface, as is known in the art.For example, the electrolyte may comprise a stabilized zirconia, such asyttria or scandia stabilized zirconia, and/or a doped ceria, such assamaria or scandia doped ceria, the anode electrode may comprise anickel cermet, such as a nickel-stabilized zirconia and/or nickel-dopedceria cermet, and the cathode electrode may comprise a conductiveperovskite material, such as lanthanum strontium manganate. Each of theinterconnects 101A-101L may comprise an electrically conductivematerial, such as metal (e.g., a chromium-iron alloy, such as 4-6 weightpercent iron, optionally 1 or less weight percent yttrium and balancechromium alloy), and may electrically connect the anode or fuel-side ofone fuel cell to the cathode or air-side of an adjacent fuel cell. Theinterconnects 101 may also separate fuel, such as a hydrocarbon fuel,flowing to the anode-side of one cell in the stack 100 from oxidant,such as air, flowing to the cathode-side of an adjacent cell in thestack 100. Each interconnect 101 may be sealed or otherwise mechanicallyadhered to a surface of one or both of the adjacent fuel cells 102 inthe assembled fuel cell stack 100.

The fuel cell stack 100 typically includes at least one internal fluidconduit, such as conduits 106 shown in FIGS. 1A-1C. The conduits 106 mayextend through multiple layers of the stack 100, and preferably extendthrough the entire stack 100. The conduits 106 may be formed by holes oropenings that are provided through the interconnects 101A-101L as wellas through the fuel cells 102 provided between the interconnects. Theopenings may be aligned with each other such that when the stack isfully assembled, the openings form a continuous fluid conduit throughmultiple cells of the stack. A conduit 106 so formed (e.g., a riserchannel) may be used to carry fuel through the stack 100 so that thefuel may be conveyed to the anode sides of each of the fuel cells 102forming the stack. A second, or return conduit may be provided to removespent fuel from each cell 102 and out of the stack 100. Such a stack 100may be internally manifolded for fuel and externally manifolded for air.Thus, the stack may be open on at least two sides to allow oxidant(e.g., air) to flow across the cathode sides of each fuel cell.Alternatively, the stack may be internally manifolded for both air andfuel, in which case additional conduit(s) for bringing air to and fromthe cathode sides of each fuel cell may be provided.

FIG. 2 is a process flow diagram illustrating a method 200 forsingulating a component of a fuel cell stack using compressed fluid(e.g., pneumatic singulation) according to one embodiment. The method200 includes connecting at least one conduit 106 extending throughmultiple layers of a fuel cell stack 100 to a fluid source at step 202.The multiple layers of the fuel cell stack through which the conduit 106extends may be, for example, a plurality of interconnects 101A-101L andintervening fuel cells 102. In embodiments, the conduit 106 may extendthrough multiple adjacent interconnects 101 and fuel cells 102 in thestack 100, and in some cases, may extend through the entire stack 100.The conduit may be an internal opening or conduit, such as fuel riseropenings through a stack that is internally manifolded for fuel, asshown in FIGS. 1A-1C. The stack 100 may be placed onto a manifoldfixture 108 connected to a tube or pipe 110 that may plumb a fluid(e.g., air) to the inlet and outlet fuel holes on the bottom of thestack 100.

In step 204 of method 200, compressed fluid is applied in the conduit106 through at least one first layer of the fuel cell stack 100. Inembodiments, the compressed fluid is compressed air, which may be at apressure greater than 20 psig, such as 25 to 125 psig, for example95-110 psig. In step 206, the conduit 106 in a second (e.g., top) layerof the stack 100 is blocked while the compressed fluid is appliedthrough the at least one first layer. The pneumatic force applied to thesecond (e.g., top) layer may thus mechanically separate the second layerfrom the at least one first layer of the stack 100 (e.g., the rest ofthe stack). The second layer may then be removed from the stack in step208.

In embodiments, the pneumatic separating action may be achieved byapplying air pressure through one layer's fuel ports instantaneouslywith the adjacent layer's fuel port blocked. Low tooling costs and highyield make this a preferred method for mechanical separation. As shownin FIGS. 1A-1C, for example, compressed air at high pressure (e.g., 90psig or more) may be provided into the fuel inlet and outlet holes inthe manifold 108 or directly in the bottom of the stack such that airflows into the stack at high velocity. When, in one embodiment, the airflow through the fuel ports 106 out of the stack is interrupted byquickly blocking the airflow at the fuel ports in the top layer of thestack (outlet ports or top of riser openings), as is shown in FIG. 1B,pressure builds in the fuel cell stack. When the pressure exceeds theadhesive strength of the seal material, the top layer of the stack 100,which may include an interconnect 101 and/or fuel cell 102, pops off oris otherwise physically separated from the stack 100 and may be removed.FIG. 1C, for example, illustrates the top layer of the stack 100,specifically interconnect 101A, removed from the stack 100. All or aportion of an adjacent fuel cell 102, which may be a SOFC including theceramic electrolyte, may be adhered to the surface of the interconnect101A. Alternatively, air may be directed into the fuel port outlet andthe bottom layer (e.g., interconnect and/or fuel cell) may be removed.

In this embodiment, a continuous air-flow through the fuel risers may beinterrupted manually or by using a tool. The operator may use twofingers (e.g., thumbs) or a simple, specially-designed tool with twoplugs (shown schematically in FIG. 1B) to cover the riser openings 106in the top of the stack to pop off layers of the stack individually. Inthis way for example, a 25-cell stack can be reliably disassembled inless than a minute, which is faster than the mechanical prying method,and less prone to damaging the interconnects.

Method 200 also encompasses alternative embodiments in which the flow ofcompressed fluid is nominally off, and a burst of compressed fluid(e.g., air) is provided through the conduit in a first layer while theopenings 106 in the second layer are blocked (i.e., the conduit in thesecond layer may be blocked in step 206 before the compressed air isprovided in the conduit through the first layer in step 204). In thisembodiment, the stack may also be placed onto the manifold fixture shownin FIGS. 1A and 1B that plumbs air to the inlet and outlet fuel ports orrisers on the bottom of the stack. The upper fuel inlet and exhaustports or risers are then blocked and the stack may be pressurized usinga pneumatic valve which opens briefly (e.g., for less than 1 second,such as 0.1 to 0.5 seconds) to generate a sufficient air pressure in thefuel risers to pop off the top layer from the stack 100.

In various embodiments, fluids other than air may be utilized for thepneumatic singulation. For example, a less compressible fluid than air,such as liquid water, may be provided from the manifold into the risersto separate the stack layers. The less compressible fluid stores lessenergy than air while pressure is building and provides the same forcesand pressure as air without the large release of energy.

FIG. 3 schematically illustrates a further embodiment method forsinglulating a fuel cell stack using inductive heating. According tothis embodiment, induction heating may introduce rapid local heating andthus induce thermal shock within one or more components of a fuel cellstack 100. Induction heating is a process in which heat can be rapidlyand controllably applied to a metal part. It is based on the principlethat a changing electric current passing through a coil causes achanging magnetic field in the area around the coil. If a metal part isplaced in the vicinity of this changing magnetic field, a changingelectric current is induced in the part, giving rise to rapid heating.As shown in FIG. 3, an induction heating coil 302, which may be coupledto a power supply 304, is placed near a fuel cell stack 100. The fuelcell stack 100 may be similar to the stack 100 described above inconnection with FIGS. 1A-1C. The induction heating coil 302 may induce arapid temperature rise in a part of the fuel cell proximate to the coil302. This rapid temperature rise may thermally shock the part, causinguneven thermal expansion and cracking a seal (e.g., a glass or glassceramic oxide seal, such as a silicon oxide based seal) securing thepart, such as interconnect 101A, to the rest of the fuel cell stack 100.In this way, the part, such as an interconnect 101A, can be reliablysingulated. Metal components such as a conventional interconnect havehigh induction susceptibility and may thus rise in temperature much morerapidly than neighboring components, such as the seal (e.g., oxide seal)and ceramic fuel cell components. Due to the mismatch in the coefficientof thermal expansion, cracking occurs between the oxide high temperatureadhesive and the metal interconnect, thus separating them elegantlywithout damaging the interconnect.

FIG. 4 is a process flow diagram illustrating an embodiment method 400for singulating a fuel cell stack by annealing in an environmentcontaining a reducing gas (e.g., hydrogen). This method 400 may be usedto separate multiple layers of a stack 100 at the same time. The method400 includes introducing a fuel cell stack 100 to a reducing gas (e.g.,hydrogen) containing environment at elevated temperature in step 402.Under a high temperature environment, hydrogen gas molecules maypenetrate, attack and weaken the seal material, such as an oxideadhesive seal material, thereby taking away its bonding function. Forexample, the stack may be placed in a furnace in a dry (or moist)atmosphere comprising hydrogen (or other reducing gases, such as carbonmonoxide, forming gas, or mixtures of reducing gases) and heated to hightemperature (e.g., in the range 850° C. to 1450° C., such as 900-1100°C., such as 950-1050° C., such as 950° C.). Preferably, the hydrogen isprovided both inside and outside of the stack 100. That is, the stack100 may be immersed in the hydrogen atmosphere. This hydrogen annealingstep may reduce an oxide within and/or on the surface of the cellcomponents, such as a chromium oxide on a surface of a Cr—Fe alloyinterconnect. These oxides help gas permeation through these componentsand help maintain the dimensional stability of the components. After thehydrogen annealing step at elevated temperature, one or more componentsmay be removed from the stack at step 404.

In an alternative embodiment of a singulation method, the fuel cellstack 100 may be subjected to an environment containing one or morespecific acids or bases for selective removal of a sealant material. Inone embodiment, the stack 100 may be placed in a chemical stripping bathdesigned to specifically attack (i.e., selectively etch) a seal material(e.g., an oxide seal material), but not the metal material (e.g., Cr orCr—Fe alloy) of the interconnects. Hydrofluoric acid (HF) may be used asthe selective oxide etching material. I-1F strongly attacks oxides, suchas silica and other oxides used for typical SOFC seals, and only slowlyattacks the Cr—Fe—Y or Cr—Fe base metal alloy of the IC component. Otherchemicals, such as nitric acid, hydrochloric acid, sulfuric acid,phosphoric acid, sodium hydroxide, potassium hydroxide, lithiumhydroxide, and molten salts such as chlorides (NaCl, KCl, MgCl₂, CaCl₂),fluorides, iodides, bromides, and/or other organic or inorganic salts,ceric ammonium nitrate, perchloric acid, and/or potassiumhexacyanoferrate, could also be utilized.

FIG. 5 schematically illustrates yet another method for singulating acomponent of a fuel cell stack by directing radiation energy at aportion of the stack. In embodiments, the radiation energy may induceuneven heating in the stack, such that one portion of the stack isheated to a higher temperature (e.g., at least 100° C. more) thananother portion of the stack. For example, the top of the stack may beheated to a higher temperature than the bottom of the stack, orvice-versa. As shown in FIG. 5, at least one radiation energy source 502may direct a beam 504 of radiation energy to a portion of the stack 100,such as the top of the stack. The radiation energy induces non-uniformheating in a portion of the stack, causing the seals to break and theinterconnects 101 to separate (i.e., the stack to fall apart). Theradiation energy may induce thermal shock in the targeted portion of thestack 100. The targeted portion of the stack may be heated in atemperature range of 850° C. to 1450° C., such as 900-1100° C., such as950-1050° C. In embodiments, the at least one radiation energy source502 may comprise an infrared radiation source (e.g., IR lamp) thatdirects a beam of infrared energy at a portion of the stack. In variousembodiments, the at least one radiation energy source 502 may be asource of microwave energy that directs a beam of microwave energy at aportion of the stack. In still further embodiments, the at least oneradiation energy source 502 may be a laser source that directs a beam oflaser energy at the stack.

In further embodiments, a method for singulating a component of a fuelcell stack includes directing acoustic energy at a portion of the stack.An acoustic energy source (e.g., a sonic source, such as an ultrasonictransducer) may be used to direct acoustic energy at the stack. A highfrequency sound may be used to shatter the seals. A single frequency orset of frequencies or spectrum of frequencies may be selected such thatthe seals are reliably destroyed but the interconnects are not damaged.

Typically, the interconnects may be cleaned after singulation. Much ofthe material clinging to the interconnects may be brushed off. However,as discussed above, ceramic electrolyte material (e.g., stabilizedzirconia, such as yttria or scandia stabilized zirconia, and/or dopedceria, such as samaria or scandia doped ceria) adjacent to the sealmaterial is typically well adhered to the interconnect. Furthermore,optional intermediate electrical contact layers or parts ofmulti-component interconnects (if present) may also need to be removedfrom the interconnects. Various embodiments include methods to removethis material that do not warp or otherwise damage the interconnect.

A first embodiment method includes introducing a part (e.g., aninterconnect) to a reducing gas (e.g., hydrogen) containing environmentat elevated temperature. This method may be similar to method 400described above in connection with FIG. 4. For example, the one or moreinterconnects may be placed in a furnace in a thy (or moist) atmospherecomprising hydrogen (or other reducing gases, such as carbon monoxide,forming gas, or mixtures of reducing gases) and heated to hightemperature (e.g., in the range 850° C. to 1450° C., such as 900-1100°C., such as 950-1050° C., such as 950° C.). This method may be performedafter the interconnect(s) have been singulated from the stack, orsimultaneous with the singulation process. Subjecting theinterconnect(s) to a high-temperature, reducing gas environment causesthe electrolyte and other debris material to soften, and thus be moreeasily removed mechanically and/or by etching.

A further embodiment method for removal or electrolyte material andother debris from a part (e.g., an interconnect) includes inductivelyheating the part before removing the electrolyte material and/or otherdebris. This method may be similar to the inductive heating singulationmethod described above and illustrated in FIG. 3. This method may beperformed after the interconnect(s) have been singulated from the stack,or simultaneous with the singulation process. Inductively heating theinterconnect may thermally shock the interconnect which may facilitateremoval of electrolyte material and/or other debris mechanically and/orby etching.

A further embodiment method for removal of electrolyte material andother debris from a part (e.g., an interconnect) includes directingradiation energy at the part to heat the part. This method may besimilar to the singulation method using radiation energy described aboveand illustrated in FIG. 5. This method may be performed after theinterconnect(s) have been singulated from the stack, or simultaneouswith the singulation process. Heating the interconnect with radiationenergy, such as IR, microwave, and/or laser energy, may thermally shockthe interconnect which may facilitate removal of electrolyte materialand/or other debris mechanically and/or by etching.

Various embodiments may also utilize a slow heating process. The partmay be heated with a furnace, IR, microwave, or laser radiation, (e.g.,in the range 850° C. to 1450° C., such as 900-1100° C., such as950-1050° C., such as 950° C.), but more slowly than the heating ratenecessary for thermal shock. A scraping tool may then used to scrape offoxide seal and electrolyte debris while the oxide seal is melted.

A last step to achieving a clean interconnect may be removing the oxide(e.g., Cr oxide) that grows on the fuel side of the IC and any residualoxide seal material or electrolyte material on the interconnect. Thishas previously been done using grit blasting. However the grit blastingprocess is costly, time consuming, difficult to control, and can causedamage to the part by inducing camber and excessive erosion of the part.

Various embodiments include methods for removing the varioushigh-temperature seals, adhesive, protective coating layer and otherresidual material (e.g., oxide material) from a part (e.g., aninterconnect) that does not require grit blasting the part.

In a first embodiment method, a part from a fuel cell stack (e.g., aninterconnect) may be chemically treated to remove residual materials,such as seal material and/or a protective oxide layer. Oxides coveringan interconnect, for example, may be removed by dipping the interconnectin a solution containing specific acids or bases for selective removal(i.e., etching) of various oxides and coating materials. The chemicalstripping bath is designed only to attack oxide material, such as asilicon oxide based glass seal material, residual electrolyte, Cr oxide,but not Cr metal or the Cr—Fe alloy of the interconnect.

For example, hydrofluoric acid (HF) may be used to selectively etch theceramic electrolyte by weakening the electrolyte by a grain boundaryattack process. HF strongly attacks oxides, such as those used fortypical SOFC electrolytes (e.g., stabilized zirconia or doped ceria),seals, and only slowly attacks the Cr—Fe—Y or Cr—Fe base metal alloy ofthe interconnect component. Other acids, such as nitric acid,hydrochloric acid, sulfuric acid, phosphoric acid or their mixturescould also be used as cleaning agents for the stack oxides. Basicsolutions such as sodium hydroxide, potassium hydroxide, lithiumhydroxide, and molten salts such as chlorides (NaCl, KCl, MgCl₂, CaCl₂),fluorides, iodides, bromides, and/or other organic or inorganic saltsmay also be effective cleaning agents as well.

Ceric ammonium nitrate, perchloric acid, and/or potassiumhexacyanoferrate may be used to etch the Cr oxide that forms on thechromium alloy interconnect surfaces. However, these etches should betimed to prevent also etching the Cr alloy interconnect. The seal andelectrolyte etch (e.g., HF etch) may be conducted before or after thechromium oxide (chromia) etch.

FIG. 6 illustrates the effect of a HF treatment on a fuel cellelectrolyte debris 602 which adheres to the interconnect 101. As can beseen in FIG. 6, a 3 hour soak in a 20% HF solution turns the electrolytedebris 602 into a white powder which can then be removed mechanicallyand/or by etching. Chromium oxide 603 which covers the interconnect, incontrast, is not affected by the HF solution. Thus, treatment with HF isan effective method for removing electrolyte 602 from an interconnect101.

An electrochemical method may also be used to remove debris, such asoxide debris, from a part (e.g., an interconnect). In one embodiment, aCr oxide covered interconnect is placed in a molten salt bath asdescribed above. An electrode (such as a graphite electrode) is alsoplaced in the bath with the interconnect. An electric current is appliedbetween the interconnect (which functions as an electrode) and the otherelectrode (e.g., the graphite electrode) in the bath. The Cr oxide maythereby be reduced, removing it from the interconnect. Molten salts canbe used above their melting temperature, and preferably up to 1000° C.Alternatively, molten hydroxides can be used in this process.

The aforementioned methods may be combined with mechanical methods(e.g., scraping) to enhance their effectiveness of cleaning and removingoxides from stack components.

In further embodiments, an acoustic shock from a sonic power source maybe used to shatter oxide seals which are adhered to a part (e.g., aninterconnect). High frequency acoustic energy may be directed at theinterconnect to shatter the seal material adhered to the interconnect. Asingle frequency or set of frequencies or spectrum of frequencies may beselected such that the seals are reliably destroyed but theinterconnects are not damaged.

In still further embodiments, the part, such as an interconnect, may beheated, such as via induction, IR, laser, microwave heating, etc., asdescribed above. The heating may induce thermal shock in the part, whichmay enable residual materials to be easily cleaned from the part.

Benefits of the various embodiment methods for refurbishing a componentof a fuel cell stack described herein may include one or more of thefollowing:

1. Lower cost per part,

2. Higher yield (i.e., less damage to the interconnects),

3. Increased scalability,

4. Increased reliability,

5. Less change to critical dimensions of the interconnect, such as flowchannel geometry,

6. Easier to automate.

While components, such as interconnects and electrolytes, of a solidoxide fuel cell stack were described above in various embodiments,embodiments can include any other fuel cell components or interconnects,such as molten carbonate or PEM fuel cell components or interconnects,or any other metal alloy or compacted metal powder or ceramic objectsnot associated with fuel cell systems.

The foregoing method descriptions are provided merely as illustrativeexamples and are not intended to require or imply that the steps of thevarious embodiments must be performed in the order presented. As will beappreciated by one of skill in the art the order of steps in theforegoing embodiments may be performed in any order. Words such as“thereafter,” “then,” “next,” etc. are not necessarily intended to limitthe order of the steps; these words may be used to guide the readerthrough the description of the methods. Further, any reference to claimelements in the singular, for example, using the articles “a,” “an” or“the” is not to be construed as limiting the element to the singular.

The preceding description of the disclosed aspects is provided to enableany person skilled in the art to make or use the present invention.Various modifications to these aspects will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other aspects without departing from the scope of theinvention. Thus, the present invention is not intended to be limited tothe aspects shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. A method of singulating a fuel cell stackcomprising a first end, a second end and a stacking dimension betweenthe first end and the second end, a plurality of interconnects and aplurality of solid oxide fuel cells, each fuel cell positioned betweenadjacent interconnects along the stacking dimension of the fuel cellstack, and an internal conduit extending from the first end to thesecond end, through the plurality of interconnects and fuel cells, forconveying a fuel to or spent fuel from the plurality of fuel cells, themethod comprising: connecting a fluid source to the internal conduit atthe first end of the stack; applying fluid in the conduit through theplurality of interconnects and fuel cells; and blocking the conduit in afirst interconnect at the second end of the stack while leaving theconduit unblocked in at least one second interconnect in the stack suchthat a fluid pressure within the stack exceeds an adhesive strength of asealing material in the stack, causing the first interconnect at thesecond end of the stack to completely separate from the fuel cell stack.2. The method of claim 1, wherein the fluid comprises a compressedfluid.
 3. The method of claim 2, wherein the fluid comprises air orwater.
 4. The method of claim 3, wherein the fluid comprises the airhaving a pressure greater than 20 psig.
 5. The method of claim 4,wherein the air has a pressure between 90 and 125 psig.
 6. The method ofclaim 1, wherein the fluid is continuously applied through the conduitor the fluid is applied in one or more bursts.
 7. The method of claim 1,further comprising removing debris from the interconnect separated fromthe stack, wherein the debris comprises at least one of electrolytematerial, seal material and chromium oxide material.
 8. The method ofclaim 7, wherein removing the debris comprises non-mechanically removingat least part of the debris from the interconnect.
 9. The method ofclaim 8, wherein the step of non-mechanically removing at least part ofthe debris comprises removing the debris by at least one of inductiveheating, radiative heating, thermally heating in a reducing gascontaining environment, chemical wet etching, or acoustic energy. 10.The method of claim 9, wherein a first part of the fuel cell debris isnon-mechanically removed from the interconnect.
 11. The method of claim10, further comprising removing a second part of the debris bymechanical scraping.
 12. The method of claim 11, wherein substantiallyall of the debris is removed from the interconnect without grit blastingthe interconnect.
 13. The method of claim 1, wherein the plurality ofinterconnects comprise chromium-iron alloy interconnects.